1. Field of the Invention
The present invention relates to force-applying tools or mechanisms and, in particular, to mechanisms for providing a mechanical advantage such that the force delivered to a workpiece is a large multiple of the force input by a user.
2. Description of the Prior Art
Various types of pivoting lever-type tools are available, such as pliers, cutters, crimpers, spreaders and the like, which essentially operate on the basis of a lever action, the lever being arranged so that the tool can deliver an output force which is greater than the input force applied by a user. In general, the leverage or mechanical advantage is a function of the handle length, so that as the force requirement increases the handle length must be extended to generate the required output force. This effectively limits the amount of output force which can be practicably produced.
It is known to provide a ratcheting-type action in pivoting-jaw tools, such as cutters and the like, whereby repeated opening and closing of the handles is required to effect a movement of the jaws through a predetermined angle. But this does not significantly increase the force which can be applied with any one handle manipulation.
In general, the average ratio of input to output force in a pivoting handle tool is the inverse of the distance of the handle stroke. Various types of compound linkages have been provided in hand tools, some of which provide very high force multiplication at or near the end of the handle stroke. For example, Vise-Grip pliers can provide, at clamping, a theoretically infinite ratio of input to output force. But such prior tools, while they may produce a relatively high average ratio of input to output force, do not produce very high ratios until near the end of the handle stroke. It is desirable in certain applications, such as the cutting of thick cables, steel pins or the like, to be able to produce an output force on the workpiece of several thousand pounds and, in particular to achieve a very high ratio of input to output force throughout the handle stroke. Heretofore, there has not been provided any tool which can produce this substantially constant high ratio of input to output force even at the beginning of the handle stroke.